= SV8 specification draft =

Nota : All fields, unless explicitely specified otherwise are read and written in Big-Endian order, independently of the underlying architecture.

== File magic number ==

Magic number is on 32bits and is equal to 'MPCK' or 0x4D50434B[[BR]]
New value so old decoders will happily skip such files.

== Block formatting ==

All blocks are formated using Key / Length / Value.[[BR]]
Key is 16 bits long. It's the block ID.[[BR]]
Length is a variable size field using the same values as [http://svn.mplayerhq.hu/mplayer/trunk/DOCS/tech/nut.txt?view=markup nut] :[[BR]]
{{{
bits, big-endian
0xxx xxxx                                           - value 0 to  2^7-2
1xxx xxxx  0xxx xxxx                                - value 0 to 2^14-2
1xxx xxxx  1xxx xxxx  0xxx xxxx                     - value 0 to 2^21-2
1xxx xxxx  1xxx xxxx  1xxx xxxx  0xxx xxxx          - value 0 to 2^28-2
...
}}}

The length is the size of the block in bytes, including the key and size fields. So the minimum length of a block is 3 bytes.[[BR]]
The value is the block content. Its size can be 0.[[BR]]
All unused bits in a block MUST be 0.[[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' ||
|| Key || 16 || "EX" ||
|| Length || n*8; 0 < n < 10 || 0x1A ||
|| Value || Length * 8 || "example" ||


== Summary of reserved block keys ==

|| '''Block name''' || '''Key''' || '''Mandatory''' ||
|| Stream information || SI || yes ||
|| Encoder information || EI || no ||
|| Audio data || AD || yes ||
|| Seek Pointer || SP || no ||
|| Seek Table || ST || no ||
|| Edition || ED || no ||
|| Stream End || SE || yes ||

== Stream information block ==

This block key is "SI".[[BR]]
This block contains the informations needed to decode the stream. This block is mandatory and must be written before the first audio block.[[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| CRC || 32 ||  || CRC 32 of the block (this field excluded). 0 = invalid ||
|| Info length || n*8; 0 < n < 10 ||  || length (in bytes) from this field (included) to the ReplayGain version field ||
|| Stream version || 8 || 8 || bitstream version ||
|| Sample count || n*8; 0 < n < 10 ||  || number of samples in the stream. 0 = unknow ||
|| Sample frequency || 3 || 0..7 || see table below ||
|| Channel count || 4 || 1..16 || number of channels in the stream ||
|| Max used bands || 5 || 1..32 || maximum number of bands used in the file ||
|| MS used || 1 ||  || MidSideStereo ||
|| Audio block frames || 3 || 0..7 || number of frames in an audio block is : 4^Value^ (1..16384) ||
|| ReplayGain version || 8 ||  || The replay gain version - must be aligned on a byte - ||
|| Title gain || 16 ||  || The loudness calculated for the title, ''and not the gain that the player must apply'' ||
|| Title peak || 16 ||  ||  ||
|| Album gain || 16 ||  || The loudness calculated for the album ||
|| Album peak || 16 ||  ||  ||

Do we need to specify the channel position ? Is there standard positions / order of the channels ?

Frequency table
|| '''Value''' || '''Frequency (Hz)''' ||
|| 0 || 44100 ||
|| 1 || 48000 ||
|| 2 || 37800 ||
|| 3 || 32000 ||

The CRC used is this one : [http://www.w3.org/TR/PNG/#D-CRCAppendix http://www.w3.org/TR/PNG/#D-CRCAppendix].

The replay gain values are stored in dB in Q8.8 format (maybe Q7.9 or relative to the max value for the bitdepth is better ?).[[BR]]


== Encoder infomations ==

This block key is "EI".

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| profile used || 4 || 0..15 ||  ||
|| PNS used || 1 ||  ||  ||
|| Unused || 3 ||  || must be 0 ||
|| MajorNumber || 4 ||  ||  ||
|| MinorNumber || 8 ||  || even = release, odd = unstable ||
|| Implementation || 4 ||  ||  ||
|| Build || 8 ||  ||  ||

== Audio data block ==

This block key is "AD".[[BR]]
This block contains audio frames. The first frame is a key frame.[[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| audio frames || ? ||  || n (or less if last block) frames of audio data as defined in SI block ||


== Seek Pointer Block ==

This block key is "SP".[[BR]]
This block contains a pointer to the seek table block.
|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| pointer || n*8; 0 < n < 10 ||  || number of bytes from this block header to the "ST" block header ||

== Seek Table Block ==

This block key is "ST".[[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| Seek Count || n*8; 0 < n < 10 ||  || number of seek elements in this table ||
|| Seek Distance || 4 || 0..15 || distance between referenced blocks = 2^Value^ ||
|| Seek Datas || ? ||  ||  ||

Format of seek datas :[[BR]]

- The reference for the seek offset is the musepack magic number[[BR]]
- The first 2 values are stored using the same code as the block length code.[[BR]]
- The next values are coded as :[[BR]]
{{{
code = value(n) - 2*value(n-1) + value(n-2)
code <<= 1;
if (code < 0)
  code = -code | 1;
}}}
code is sent as [http://en.wikipedia.org/wiki/Golomb_code golomb code] with M = 2^12^.


== Security Block ==

Checksum (MD5, SHA1) or error correcting code (LDPC).[[BR]]
To be defined later. May be better to keep security features external only.

== Edition Block ==

The SV8 stream allow only to start decoding on first block frame, so cutting the stream require to cut on block boundaries. This block 
provides more precise cutting possibilities.[[BR]]
This block must be written before the first audio block.[[BR]]
This block key is "ED"[[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| Beginning silence || n*8; 0 < n < 10 ||  || number of samples to skip at the beginning of the stream ||
|| End silence || n*8; 0 < n < 10 ||  || number of samples to skip at the end of the stream ||

== End Block ==

This block key is "SE".[[BR]]
The recommanded block lenth is 3 bytes.[[BR]]
This block is mandatory and must be the last block of the stream. Tags are written after this block.

== Streaming ==

This file format can be used for streaming. The "SI" block is used as synchronization marker. The decoder will scan for a "SI" block and check the block CRC. Once the decoder is synchronized, it will start decoding. It's up to the streaming server to choose when to send "SI" block.[[BR]]
There is currently no way to send tags during playback. This must be changed (a tag block ?).

== Tags ==

No block must be written after the end block to allow tagging by other applications.[[BR]]
Remarks about tagging? Incompatibilities?[[BR]]